The government's Help to Buy scheme contributed to a surge in first-half sales by housebuilder Barratt Developments.

In a trading update, Britain's biggest housebuilder by volume said total forward sales increased by 71% to £1.27bn in the six months to the end of December.

The company completed sales on 6,195 properties – 1,001 more than in the same period a year earlier. Excluding joint ventures, 29% of completed sales were supported by Help to Buy, in which the government guarantees part of a homebuyer's deposit.

Barratt expects its total average selling price on completions to rise 13.7% to £211,000 in the first half after a switch into more profitable family homes and away from high density city-centre flats. Underlying sales prices are also on the rise because rising demand has reduced the need to offer incentives to buyers

Mark Clare, chief executive, said that improved financial performance left the group well placed for the rest of the year and beyond. "As a result of the continued recovery of the housing market across all regions and our £3.1bn investment in new land over the last four years, we have been able to increase materially the number of new homes being built and our profitability."

Business at Barratt and other housebuilders has recovered sharply after years in the doldrums following the financial crisis. Chancellor George Osborne launched Help to Buy last year in a bid to revive the housing market and support the wider economy. But some economists and housing experts have warned the scheme is inflating a house-price bubble that could leave buyers struggling if prices fall sharply.

Barratt said it would continue to buy land for further development after snapping up 11,394 plots in the first half, up from 9,320 a year earlier.

Barratt shares fell 0.5% to 375p by 9am on Tuesday.

Separately, Countrywide, Britain's largest estate agent by revenue, said it expected to 2013 profit at the top end of its expectations after income rose 11% in the year to the end of December.